The present invention relates generally to the field of power electronic devices such as those used in power conversion or applying power to motors and similar loads. More particularly, the invention relates to optimizing the flow of cooling air across motor drive heat sinks.
In the field of power electronic devices, a wide range of circuitry is known and currently available for converting, producing, and applying power to loads. Depending upon the application, such circuitry may convert incoming power from one form to another as needed by the load. In a typical arrangement, for example, constant (or varying) frequency alternating current power (such as from a utility grid or generator) is converted to controlled frequency alternating current power to drive motors, and other loads. In this type of application, the frequency of the output power can be regulated to control the speed of the motor or other device. Many other applications exist, however, for power electronic circuits which can convert alternating current power to direct current power (or vice versa) or that otherwise manipulate, filter, or modify electric signals for powering a load. Circuits of this type generally include rectifiers (converters), inverters, and similar switched circuitry. For example, a motor drive will typically include a rectifier that converts AC power to DC. Power conditioning circuits, such as capacitors and/or inductors, are often employed to remove unwanted voltage ripple on the internal DC bus. Inverter circuitry can then convert the DC signal into an AC signal of a particular voltage and frequency desired for driving a motor at a particular speed or torque. The inverter circuitry typically includes several high power semiconductor devices, such as insulated-gate bipolar transistors (IGBTs), silicon controlled rectifiers (SCRs) and diodes controlled by drive circuitry.
The power semiconductors detailed above will typically generate substantial amounts of heat, which must be dissipated to avoid damaging heat sensitive electronics. Typically, therefore, some form of cooling mechanism may be employed to enhance heat extraction and dissipation. Often, the circuitry is packaged together as a unit with a built-in cooling channel that provides cool air to several components. It is now recognized that, because the air within the channel is heated as it travels through the channel, components near the exhaust end of the air channel will usually experience a diminished cooling effect. Therefore, as packaged control units become more compact, the need for efficient heat dissipation becomes more critical. Additionally, as the workload or motor speed changes, the temperature of the semiconductors generally increases, causing higher failure rates and reduced reliability. The output of the unit is often, therefore, limited by the maximum temperature that the unit can handle without substantially increasing the risk of failure. A more effective cooling mechanism would, therefore, allow the motor drive to operate at higher motor power levels. Therefore, it may be advantageous to provide a motor drive with an improved cooling mechanism. In particular, it may be advantageous to provide a cooling mechanism which provides a reduced air flow resistance and increased air flow while maintaining a high level of thermal performance.